The invention relates to the field of the cooling of the combustion engines of motor vehicles such as private cars, trucks, buses or site plant. A cooling circuit generally passes through a number of mechanical parts that are to be cooled and may also be used to heat up certain elements that consume heat energy, these being connected by pipes or other flexible or rigid ducts through which a heat-transfer fluid commonly known as liquid coolant flows.
The invention relates more specifically to a special arrangement of the cooling circuit that is aimed at dissipating the heat to the atmosphere more effectively and at improving the overall efficiency of heat exchanges between the various mechanical parts of the motor vehicle and those elements of the motor vehicle that require heating.
In general, a motor vehicle combustion engine cooling circuit comprises a so-called “high temperature” main circuit used to cool and to regulate the temperature of the combustion engine. A main circuit such as this thus comprises a radiator capable of removing the heat energy given off by the engine and carried by the coolant. This radiator allows exchange of heat with an ambient air flow that is dependent on the speed of the vehicle and/or on whether or not the fan is running. A pump also forms part of this main circuit and adapts the rate of flow of liquid coolant through the circuit. A thermostat arranged on the main circuit allows the radiator to be short circuited and thus allows the coolant to heat up more quickly.
What is more, the main engine cooling circuit may also be used for various applications and, in particular, to cool various pieces of equipment. Included among these elements are, for example and in particular, a condenser of the air-conditioning circuit that air conditions the cab or cabin of the motor vehicle, and also an exchanger in the engine cooling oil circuit, the gearbox cooling oil circuit, the supercharging or boost compressed air circuit or alternatively the circuit that recirculates the exhaust gases, also known as the EGR (Exhaust Gas Recirculation) circuit.
In order to cool these various elements, secondary circuits may therefore be connected to the main cooling circuit. The liquid coolant may, in a first embodiment as described in document FR 2 832 185, pass through a radiator dedicated to this secondary loop in order to drop its temperature below that of the coolant in the main circuit. The coolant then passes through the equipment that is to be cooled. A secondary loop such as this is generally known by the name of “low temperature loop” because the temperature of the coolant is lowered before it is used to cool a piece of equipment.
However, the various items of equipment that need to be cooled do not need low-temperature cooling and may be cooled by the main so-called “high-temperature” circuit. Thus, the exhaust gas recirculation (EGR) system may be cooled directly using the coolant flowing through the main loop, the maximum temperature of which is of the order of 110° C. This is because the circuit for cooling the recirculated gases needs to be able to drop the temperature of the exhaust gases from a temperature of 600° C. to around 180° C., and a fluid at 110° C. is therefore able to perform such cooling. The same is true of the supercharging air cooling circuit that needs to be capable of cooling the compressed air, which leaves the compressor at an outlet temperature of around 200° C. to 250° C.
Thus, in this prior art, the ventilation air, in the radiators, removes all of the heat energy generated by the heat sources. The air cannot, however, be heated above the temperature of the coolant present in the main circuit.
According to another prior art, the secondary circuits may also be devoid of radiators. In this case, the radiator of the main circuit has to remove the additional heat supplied to the coolant.
However, it then becomes necessary to increase the heat exchange area of the radiator, and this may prove to be incompatible with the space available at the front end of the vehicle.
Also known, and as described in document U.S. Pat. No. 5,244,256, are motor vehicle cooling circuits comprising two separate cooling loops, one specifically devoted to cooling the exhaust gas recirculation (EGR) device.
However, a set-up such as this entails duplicating elements specific to each independent cooling loop, such as pumps and expansion vessels.
Thus, it is desirable to improve the cooling of a thermal installation formed of an engine and all its auxiliary equipment.
It is also desirable to reduce the number of elements, particularly by using a single pump, a single expansion vessel and a single degassing system for both cooling circuits.
The invention therefore relates, according to an aspect thereof, to a motor vehicle combustion engine cooling circuit comprising a main loop comprising a first exchanger that collects the heat from a first heat source. This exchange is generally performed within passages created in the engine block in the region of the cylinders or in the cylinder head in the region of the combustion chambers. The main loop also comprises a first radiator and a pump that enables a sufficient flow rate to be created that the heat energy given off by the combustion within the engine can be removed. The various elements of the main loop are connected in series using hoses through which the liquid coolant can flow. Under normal operating conditions, the temperature of the liquid is kept at a temperature lower than or equal to a predetermined threshold value.
According to an aspect of the invention, the cooling circuit is characterized in that it comprises a first bypass of the main loop arranged in parallel with the first radiator. This first bypass comprises, in succession, in the direction in which the coolant flows, a second exchanger collecting heat from a second heat source and a second radiator, these being connected in series by means of hoses through which the coolant can flow. Under normal operating conditions, the temperature of the coolant leaving the second exchanger is raised to a temperature higher than or equal to the predetermined threshold value.
In other words, the coolant heated as it passes through the ducts in the combustion engine is used to cool or heat directly specific equipment of the vehicle using a coolant at a higher temperature. The fact of the matter is that some equipment does not require the use of a coolant the temperature of which is regulated below the predetermined threshold value. The coolant in this bypass is therefore raised to a temperature higher than that of the coolant in the main loop. Thus, the main loop can be termed a “high-temperature” loop, while the bypass can be termed “a very-high-temperature” bypass.
More specifically, in the main loop, the temperature of the coolant needs to be kept below the predetermined threshold value of about 110° C. Overheating of the engine could have detrimental effects on the engine gaskets or alternatively on the internal clearances that allow the pistons to slide inside the cylinders, and in general on the lubrication of the various mechanical moving parts. However, the various pieces of equipment connected to this “very-high-temperature” bypass do not require such temperature regulation and are able to withstand far higher temperatures. Thus, the temperature of the coolant leaving the second exchanger is higher than the temperature of the coolant in the main circuit, at nominal speed and load.
A cooling circuit such as this therefore makes it possible to improve the exchange of heat between the ventilation air passing through the radiators and the coolant by virtue in particular of the increase in temperature difference between these two fluids.
As has already been mentioned, the heat sources, some of the heat energy from which is removed in the second exchanger, may be of differing natures. The various sources may therefore be used independently or in combination according to various embodiments of the second exchanger.
According to a first embodiment of the invention, the second heat source of the second exchanger may comprise a circuit of the exhaust gas recirculation system.
In this case, the second exchanger is, for example, of the liquid/gas type in which the gases released during combustion within the engine are collected and cooled using the exchanger reducing them from a temperature of about 600° C. to about 180° C. This reduction in temperature is due to the exchange of heat with the liquid coolant entering the first bypass of the main loop of the cooling circuit. On leaving the second exchanger, the liquid coolant is therefore at a higher temperature than in the main circuit.
According to a second embodiment, the second heat source of the second exchanger may comprise a circuit of the combustion engine lubricating oil. In this case, the second exchanger is of the liquid/liquid type in which the liquid coolant is heated by the engine lubricating oil.
According to a third embodiment, the second heat source of the second exchanger may comprise a supercharged (boost) compressed air circuit.
In this case, the second exchanger is, for example, of the liquid/gas type in which the liquid coolant stores heat energy carried by the air compressed beforehand by a device of the compressor or turbocharger type since the temperature of the air leaving this type of device is generally of the order of 200 to 250° C.
These various embodiments may, when combined, be incorporated into one single multiple-duct exchanger capable of carrying several fluids and which are separated by means of a heat-exchange surface. Numerous types of exchanger may in particular be used, for example heat exchangers of the “plate”-type or tube-type beat exchangers.
The use of a separate radiator for the bypass improves the efficiency of the exchange of heat between the air and the fluid that is to be cooled which is at a higher temperature. This is because for a given rate of flow of ventilating air, this independent radiator is able to dissipate a greater amount of heat by increasing the temperature difference between the inlet and outlet of the exchangers. In addition, this arrangement makes it possible to reduce the size of the main circuit radiator.
What is more, the radiators of the main loop and of the “very-high-temperature” bypass may be positioned in various ways relative to one another.
According to a first alternative form, these radiators may be arranged, in terms of air flow, in series. In this case, the air collected by the front end of the vehicle passes in succession between the cooling fins of the radiator of the main loop then of the first bypass. In other words, the two radiators are positioned one behind the other, for example perpendicular to the direction of travel of the vehicle that corresponds to the direction of air flow.
In this case, the air used to cool the second radiator is at a temperature higher than that of the external air, namely for example about 100° C. when the external air is at 40° C. This increase in air temperature is not, however, detrimental, because the liquid coolant flowing through the second radiator is also at a higher temperature. Thus the air, even heated, is able to cool the liquid coolant in the second radiator.
Furthermore, the second radiator preferably has dimensions smaller than or equal to those of the first radiator and thus does not increase the widthwise and heightwise size of the air collecting surface on the front end of the vehicle. Thus, for the same overall frontal surface area, a cooling circuit such as this comprising a “very-high-temperature” bypass is able to increase the dissipated thermal energy.
According to a second alternative form, the first and second radiators may be arranged, in terms of air flow, in parallel. In this case, the two radiators may be cooled by separate air flows, leading to an overall exchange area that is greater than the largest dimension of the two radiators. This arrangement does, however, improve the overall cooling efficiency since, in this case, the air flow passing through the two radiators is at the same temperature that corresponds to the temperature of the external surroundings.
The two radiators may also be cooled by one and the same flow of air which is diverted after passing through the first radiator. In this case, the air flow passing through the second radiator is at a temperature higher than that of the air flow passing through the first radiator.
In order to improve the speed at which the liquid coolant comes up to temperature in the main loop, a thermostat may be fitted to this loop in order to regulate the rate of flow of liquid coolant according to its temperature.
According to a first embodiment, the first bypass may be arranged downstream, in the direction in which the coolant flows, of the thermostat arranged on the main circuit. In this case, when the thermostat shuts off the flow of liquid coolant through the first radiator, it at the same time shuts off the flow of liquid coolant through the first bypass. The coolant is therefore not cooled and flows through the first exchanger in a closed circuit.
In a second embodiment, the first bypass may be arranged upstream, still in the direction in which the coolant flows, of a thermostat arranged on the main circuit. In this case, when the thermostat is actuated, the coolant no longer flows through the first radiator but may, however, flow through the first bypass.
Advantageously, in this case, the first bypass may comprise a second thermostat. Thus it is possible to increase the speed with which the liquid coolant is heated, by allowing it to flow only through the first and second heat exchangers without being cooled in the first and second radiators.
Furthermore, the first bypass may comprise a regulating valve. A valve such as this then allows the rate of flow of coolant through the first bypass to be regulated.
According to one particular embodiment, the cooling circuit may comprise a second bypass of the main loop, arranged in parallel with respect to the first radiator and to the first heat exchanger, it being possible for this second bypass to have, in succession, in the direction in which the coolant flows, a third radiator and a third exchanger collecting heat from a third heat source, these being connected in series by means of hoses through which the coolant can flow.
What happens is that the cooling circuit may also comprise a second bypass able to supply heat at a temperature lower than that of the first loop. This second bypass then acts as a “low-temperature” bypass. In this case, the supercharging air can be cooled notably in two stages. A first cooling using the second exchanger of the “very-high-temperature” first bypass brings about a first drop in temperature on contact with the high-temperature coolant. A second cooling of the supercharging air in the third exchanger of the second bypass profits from a low-temperature coolant. Similar cycles, which comprise using the second exchanger as a “pre-cooler” and the third exchanger as a “cooler” may also be used to cool the engine oil or the exhaust gases of the EGR system.
In practice, the first bypass may also comprise a fourth heat exchanger connected to a circuit for heating the air with which the cab or cabin of the vehicle is ventilated.
This is because, and particularly in winter, it may be necessary to heat the cab or cabin of the vehicle quickly. This heat exchanger may be arranged in parallel with the second radiator, particularly at the outlet from the second heat exchanger of the high-temperature loop. This is because in such an instance the coolant is raised to a very high temperature before it enters the fourth heat exchanger. This supply of heat energy may, in particular, improve the efficiency of the heat transfer.